The official C implementation of BLAKE3.
An example program that hashes bytes from standard input and prints the result:
#include "blake3.h"
#include <stdio.h>
#include <unistd.h>
int main() {
// Initialize the hasher.
blake3_hasher hasher;
blake3_hasher_init(&hasher);
// Read input bytes from stdin.
unsigned char buf[65536];
ssize_t n;
while ((n = read(STDIN_FILENO, buf, sizeof(buf))) > 0) {
blake3_hasher_update(&hasher, buf, n);
}
// Finalize the hash. BLAKE3_OUT_LEN is the default output length, 32 bytes.
uint8_t output[BLAKE3_OUT_LEN];
blake3_hasher_finalize(&hasher, output, BLAKE3_OUT_LEN);
// Print the hash as hexadecimal.
for (size_t i = 0; i < BLAKE3_OUT_LEN; i++) {
printf("%02x", output[i]);
}
printf("\n");
return 0;
}If you save the example code above as example.c, and you're on x86_64
with a Unix-like OS, you can compile a working binary like this:
gcc -O3 -o example example.c blake3.c blake3_dispatch.c blake3_portable.c \
blake3_sse2_x86-64_unix.S blake3_sse41_x86-64_unix.S blake3_avx2_x86-64_unix.S \
blake3_avx512_x86-64_unix.Stypedef struct {
// private fields
} blake3_hasher;An incremental BLAKE3 hashing state, which can accept any number of
updates. This implementation doesn't allocate any heap memory, but
sizeof(blake3_hasher) itself is relatively large, currently 1912 bytes
on x86-64. This size can be reduced by restricting the maximum input
length, as described in Section 5.4 of the BLAKE3
spec,
but this implementation doesn't currently support that strategy.
void blake3_hasher_init(
blake3_hasher *self);Initialize a blake3_hasher in the default hashing mode.
void blake3_hasher_update(
blake3_hasher *self,
const void *input,
size_t input_len);Add input to the hasher. This can be called any number of times.
void blake3_hasher_finalize(
const blake3_hasher *self,
uint8_t *out,
size_t out_len);Finalize the hasher and emit an output of any length. This doesn't
modify the hasher itself, and it's possible to finalize again after
adding more input. The constant BLAKE3_OUT_LEN provides the default
output length, 32 bytes.
void blake3_hasher_init_keyed(
blake3_hasher *self,
const uint8_t key[BLAKE3_KEY_LEN]);Initialize a blake3_hasher in the keyed hashing mode. The key must be
exactly 32 bytes.
void blake3_hasher_init_derive_key(
blake3_hasher *self,
const char *context);Initialize a blake3_hasher in the key derivation mode. The context
string is given as an initialization parameter, and afterwards input key
material should be given with blake3_hasher_update. The context string
is a null-terminated C string which should be hardcoded, globally
unique, and application-specific. The context string should not
include any dynamic input like salts, nonces, or identifiers read from a
database at runtime. A good default format for the context string is
"[application] [commit timestamp] [purpose]", e.g., "example.com 2019-12-25 16:18:03 session tokens v1".
This function is intended for application code written in C. For
language bindings, see blake3_hasher_init_derive_key_raw below.
void blake3_hasher_init_derive_key_raw(
blake3_hasher *self,
const void *context,
size_t context_len);As blake3_hasher_init_derive_key above, except that the context string
is given as a pointer to an array of arbitrary bytes with a provided
length. This is intended for writing language bindings, where C string
conversion would add unnecessary overhead and new error cases. Unicode
strings should be encoded as UTF-8.
Application code in C should prefer blake3_hasher_init_derive_key,
which takes the context as a C string. If you need to use arbitrary
bytes as a context string in application code, consider whether you're
violating the requirement that context strings should be hardcoded.
void blake3_hasher_finalize_seek(
const blake3_hasher *self,
uint64_t seek,
uint8_t *out,
size_t out_len);The same as blake3_hasher_finalize, but with an additional seek
parameter for the starting byte position in the output stream. To
efficiently stream a large output without allocating memory, call this
function in a loop, incrementing seek by the output length each time.
This implementation is just C and assembly files. It doesn't include a
public-facing build system. (The Makefile in this directory is only
for testing.) Instead, the intention is that you can include these files
in whatever build system you're already using. This section describes
the commands your build system should execute, or which you can execute
by hand. Note that these steps may change in future versions.
Dynamic dispatch is enabled by default on x86. The implementation will
query the CPU at runtime to detect SIMD support, and it will use the
widest instruction set available. By default, blake3_dispatch.c
expects to be linked with code for five different instruction sets:
portable C, SSE2, SSE4.1, AVX2, and AVX-512.
For each of the x86 SIMD instruction sets, two versions are available, one in assembly (with three flavors: Unix, Windows MSVC, and Windows GNU) and one using C intrinsics. The assembly versions are generally preferred: they perform better, they perform more consistently across different compilers, and they build more quickly. On the other hand, the assembly versions are x86_64-only, and you need to select the right flavor for your target platform.
Here's an example of building a shared library on x86_64 Linux using the assembly implementations:
gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.c \
blake3_sse2_x86-64_unix.S blake3_sse41_x86-64_unix.S blake3_avx2_x86-64_unix.S \
blake3_avx512_x86-64_unix.SWhen building the intrinsics-based implementations, you need to build each implementation separately, with the corresponding instruction set explicitly enabled in the compiler. Here's the same shared library using the intrinsics-based implementations:
gcc -c -fPIC -O3 -msse2 blake3_sse2.c -o blake3_sse2.o
gcc -c -fPIC -O3 -msse4.1 blake3_sse41.c -o blake3_sse41.o
gcc -c -fPIC -O3 -mavx2 blake3_avx2.c -o blake3_avx2.o
gcc -c -fPIC -O3 -mavx512f -mavx512vl blake3_avx512.c -o blake3_avx512.o
gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.c \
blake3_avx2.o blake3_avx512.o blake3_sse41.o blake3_sse2.oNote above that building blake3_avx512.c requires both -mavx512f and
-mavx512vl under GCC and Clang, as shown above. Under MSVC, the single
/arch:AVX512 flag is sufficient. The MSVC equivalent of -mavx2 is
/arch:AVX2. MSVC enables SSE4.1 by defaut, and it doesn't have a
corresponding flag.
If you want to omit SIMD code on x86, you need to explicitly disable each instruction set. Here's an example of building a shared library on x86 with only portable code:
gcc -shared -O3 -o libblake3.so -DBLAKE3_NO_SSE2 -DBLAKE3_NO_SSE41 -DBLAKE3_NO_AVX2 \
-DBLAKE3_NO_AVX512 blake3.c blake3_dispatch.c blake3_portable.cThe NEON implementation is not enabled by default on ARM, since not all
ARM targets support it. To enable it, set BLAKE3_USE_NEON=1. Here's an
example of building a shared library on ARM Linux with NEON support:
gcc -shared -O3 -o libblake3.so -DBLAKE3_USE_NEON blake3.c blake3_dispatch.c \
blake3_portable.c blake3_neon.cNote that on some targets (ARMv7 in particular), extra flags may be required to activate NEON support in the compiler. If you see an error like...
/usr/lib/gcc/armv7l-unknown-linux-gnueabihf/9.2.0/include/arm_neon.h:635:1: error: inlining failed
in call to always_inline ‘vaddq_u32’: target specific option mismatch
...then you may need to add something like -mfpu=neon-vfpv4 -mfloat-abi=hard.
The portable implementation should work on most other architectures. For example:
gcc -shared -O3 -o libblake3.so blake3.c blake3_dispatch.c blake3_portable.cThe single-threaded Rust and C implementations use the same algorithms, and their performance is the same if you use the assembly implementations or if you compile the intrinsics-based implementations with Clang. (Both Clang and rustc are LLVM-based.)
The C implementation doesn't currently include any multithreading optimizations. OpenMP support or similar might be added in the future.